Point $F$ lies on a unit circle in the xy-plane and has coordinates $\left(1,0\right)$. Point $G$ is the center of the circle and has coordinates $\left(0,0\right)$. Point $H$ also lies on the circle and has coordinates $\left(-1,y\right)$, where $y$ is a constant. Which of the following could be the positive measure of angle $FGH$, in radians?